Electric telegraph system



Sept. 29, 1953 E. P. G. WRIGHT Attorney Sept. 29, 1953 E. P. G. WRIGHT ELECTRIC TELEGRAPH SYSTEM 12 Sheets-Sheet 2 Filed Nov. l0, 1951 A Homey E. P. G. WRIGHT ELECTRIC TELEGRAPH SYSTEM sept. 29, 1.953

12 Sheets-Sheet 3 Filed NOV. 10, 19511 Attorney Sept. 29, 1953 E. P. G. WRIGHT `ELECTRIC TELEGRAPH SYSTEM :12 Sheets-Sheet 4 Filed Nov. l0, 1951 W @bk A Harney Sept. 29, 1953 E. P. G. WRIGHT 2,653,996

ELECTRIC TELEGRAPH SYSTEM Filed Nov. l0, 1951 l2 Sheets-Sheet 5 Inventor e. ma fnl-,ff

BWM/w@- ltorne y Sept. 29, 1953 E. P. G. WRIGHT ELECTRIC TELEGRAPH SYSTEM 12 Sheets-Sheet 6 Filed Nov. l0, 1951 F/G. Z

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\|I\f}. wr. E O M R 4 N u E WW o m m m W \f J kf J )Ill MMMMMM-S MMMSMMSMSSMMSMSSMSSSMSSSSS HMMMMSM MMSMMSMSMSMSMSMSSMSSSMSSSS WMMMSMM MSMMSMMSSMSMMSSMSMSSSMSSS WM SMMMSSSMMMSSSMM-MSS$MSSSMS S C M S M M M M S S S S M M M M M S S S S S S M M M M S S S M S Atlorney sept. 29, 1953 Filed Nov. lO, 1951 ELECTRIC TELEGRAPH SYSTEM E. P. G. WRIGHT F/RS T COMBI/VA TION l2 Sheets-Sheet 7 T//ME OND/Ilm OND/NON COND] NON R4 M/ugfs F2 79g man 2 3 4 5 6 7 o M M M M M M M M M 2o s 29 M M M M M M S 48 [sjf M M M M M s M 49 M M M M M s s 6e M M M M s s M se [M] M M M s s M M /oo s /08 M M s s M M M /09 M M s s M M s /29 M s s M M s M SECOND COME/NA 7/0N o s M M s s M M s M 8 S s M M s M M 9 s s M M s M s 27 s 2e s M M s M s M 30 M 47 'IS7' s 4e M M s M s M M 50 M 6e M S M S M M M 88 [M s M s M M M M /07 W] S /oe M s M M M- M M s M M M M s /26 '[Mj' M /28 S M S M Inventor Attorney Sept. 29, 1953 E. P. G. WRIGHT ELECTRIC TELEGRAPH SYSTEM l2 Sheets-Sheet 8 Filed Nov. 10, 1951 Inventork Aliorney Sept. 29, 1953 E. P. G. WRIGHT ELECTRIC TLEGRAPH SYSTEM l2 Sheets-Sheet 9 Filed Nov. 10, 1951 e. e b.'

Attorney E. P. G. WRIGHT 2,653,996 ELECTRIC TELEGRAPH SYSTEM l2 Sheets-Sheet 10 Sept. 29, 1953 Filed NOV. l0, 1951 Sept. 29, 1953 Filed NOV. l0, 1951 E. F'. G. WRIGHT ELECTRIC TELEGRAPH SYSTEM 12 Sheets-Sheet 11 ao, /o0, /20

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Sept. 29, 1953 E. P. G. WRIGHT ELECTRIC TELEGRAPH SYSTEM 12 Sheets-Sheet 12 Filed Nov. 10, 1951 Nm NW Om. QN OWN QQ en 0T E. M. 7W

A Home y Patented Sept. 29, 1953 UNTED STATES PATENT OFFICE ELECTRIC TELEGRAPH SYSTEM of Delaware Application November 10. 1951, Serial No. 255,794 In Great Britain November 8, 1950 15 Claims.

This invention relates to electric telegraph systems and similar signalling systems using two signalling conditions, called in the case of telegraphy, mark and space respectively.

Telegraph systems are known in which the code combinations used are such that an incorrectly received combination can readily be detected and either a printed indication be made that a character is incorrect, or a request for repetition of the signal combination be automatically sent back to the transmitter.

A Well known form of code for such a system is one in which the ratio of marks and spaces in each combination is always the same, for example, each character is represented by a code combination of eight elements, there being always four marks and four spaces. Alternatively, each character may be represented by a code combination of seven elements, there being always three marks and four spaces or vice versa. in a combination.

Whilst the uses hitherto proposed for these codes have been to detect the presence of an error in a received code combination, it has been necessary, in all known systems, to send back from the receiving station to the transmitting station a request for the re-transmission of the characters that were received incorrectly, usually referred to as a RQ and then for the transmitting station to retransmit the characters. Clearly this means additional channel time and it is to be noted that it is necessary to take up considerable time to identify the particular characters for which re-transmission is required both in the RQ and in the retransmission.

The present invention provides a means, not only for indicating the presence of an error, but of identifying the nature of the error so that correction of the error can be made without the necessity for any RQJ According to the present invention, characters are divided into groups and after each group of n code combinations an additional, cross-check combination is sent, the respective elements of which depend upon the relation between the numbers of marks and spaces in the corresponding elements of the code combinations of the preceding group.

The invention will be described in relation to the translation into and from a seven-element error-indicating lcode containing a constant total of three spaces and four marks.

The basic principles of the translation process may be summarised briefly as ioilows:

(c) A two-element prex is added to the original nre-element teleprinter code combination to bring the total number of elements up to seven.

(b) In the case of code combinations contain- 2 ing one, two or three spaces, the prex adds the number of spaces necessary to bring the total number of spaces up to three, no further translation being eiiected.

(c) In the case of the remaining code combinations the prex is invariable and distinct from those added in paragraph b and further translations are carried out on the original code combination before re-transmission.

These basic principles of translation are disclosed in U. S. Patent No. 2,520,142, issued to J. A, Herbst. In the circuits disclosed in this prior specification, electro-magnetic contactmaking relays are used together with mechanical input and output distributors.

An embodiment of the invention will now be described with reference to the accompanying drawings in which:

Figs. 1 to 4 together form a block schematic diagram of a circuit according to the invention for translating five element start-stop teleprinter code combinations into constant-total sevenelement combinations and for inserting a crosscheck combination after every five combinations have'been transmitted,

Figs. 5 and 6 are diagrams showing in greater detail two of the devices shown symbolically in Figs. l to 4 and 9 to 12,

Fig. 7 is a table showing the thirty-two fiveelement code combinations together with the seven-element code combinations into which and from which they are translated by means of the circuits of Figs. 1 to 4 and 9 to 13,

Fig. 8 is a table showing the various changes in circuit conditions when deriving a cross-check combination from two sample code combinations, and

Figs. 9 and 13 together form a block schematic diagram of a circuit according to the invention for converting the constant-total seven-element code combinations back into five-element startstop teleprinter code combinations, for deriving from every five received code combinations a counter-check combination, and for comparing the derived counter-check combination with that received. In order to simplify the description and drawings as much as possible, full circuit diagrams of the various gate circuits, counting chains, registers, etc. have not been given, but suitable references have been given to other specications from which full particulars may be obtained. Thus, Figs. 1 to 4 end 9 to 13 are functional in nature and are intended to show the processes involved rather than the actual means used. Thevarious symbols used in these figures will be explained as they enter the description.

Where connections are taken from one figure to another, the points where leads enter or leave a particular figure have been identied by the reference letter L and a serial number together with the figure number. It has not, however, been found practicable in many cases to allot similar positions to similarly numbered leads on adjoining sheets.

In carrying out this embodiment of the invention considerable use is made of static electrical switches. l

A static electrical switch is defined as a device having a permanently positioned electrical path the effective impedance of which may be either of two dierent values, change from the one to the other value being effected by an appropriate change in a controlling electric or magnetic field from one stable condition to another.

The term static electrical switch as used in this specification should be interpreted to include any device falling within the terms of this definition and in any case includes thermistor trigger circuits, hot or cold cathode discharge tubes, hard tube trigger circuits, cathode ray tubes and metal rectifier circuits.

Throughout the description a telegraph speed of 50 bauds is assumed.

Referring now to Figs. 1 to 4, the timing of the various stages of reception, translation and transmission is controlled by means of a time scale circuit shown in Fig. 1. This time scale circuit comprises a plurality of static electrical switches in the form of three multi-cathode gaslled discharge tubes shown as blocks CI, C2 and C3 and three gas-filled high-speed trigger tubes shown as gating devices G2, G3 and G4. The time scale circuit is connected and designed to operate in the same manner as that shown and described in detail in the specication of the co-pending application of V. J. Terry-D. S. Ridler-D. A. Weir led March 29, 1949, and bearing Serial No. 84,104. Its function is to count ve-kilocycle negative pulses applied at points marked P. As explained in the abovementioned specification, Cl is arranged to count all the pulses, C2 to count every tenth pulse and C3 to count every hundredth pulse. At any particular time after counting begins, a discharge will be present across a particular gap in each tube, which gap will depend upon the number of pulses counted and hence upon the time that has elapsed. Thus after, say, 175 pulses have been counted gap l in the hundreds tube C3 will be red together with gap 1 in the tens tube C2 and gap 5 in the units tube CI. Since there are five pulses every millisecond it will be apparent that the time interval which must elapse before the above condition can be reached is 175-;-5:35 milliseconds. In the aforesaid co-pending application, it is further explained and shown how the simultaneous ring of two or three specific gaps in respective tubes may be used to open a gating circuit at a particular time. In order to reduce the complexity of Figs. l to 4 and 9 to 13 of the present case, circuits for connecting the outputs of the counting tubes with various gates which are required to be opened at specific times have been omitted but, instead, the times at which potentials are derived from the time scale circuit are shown against various conductors connected to gates thus: TI, 2|, 4| etc. These figures are the time intervals in milliseconds after the starting of the time scale circuit. In order tc determine which gaps must be fired at a par`P ticular time, it is only necessary to multiply the time in milliseconds by five. Thus at time T2l, pulses will have been counted and the gaps fired will be gap 5 of CI, gap 0 of C2 and gap l of C3.

It is assumed that transmission of the sevenelement combinations takes place on a synchronous basis over a line or a radio path, whichever is convenient. In order to maintain the receiver in synchronism with the transmitter, a synchronising pulse is sent out at regular intervals from the transmitter as shown symbolically on the right of Fig. 2. These synchronising pulses are also directed to provide one input to a gate GI (Fig. 1). This gate requires two inputs before it can produce an output'as denoted by the figure "2 within the gate symbol. A gate of this type is disclosed in the specification of British Patent No. 636,700 and its operation is there fully explained.

The other input to gate GI is from the stop tube SP of a start-stop trigger device or iiipflop FI. This latter may comprise, for example, a pair of cold-cathode, high-speed trigger tubes interconnected in well-known manner, whereby the ring of either tube extinguishes the other. Thus, as soon as the synchronising pulse is applied to gate GI, this gate opens and causes the start tube ST to be fired, so extinguishing the stop tube. The output of tube ST allows pulses from P- to pass through gate G2 into counting tube CI, thus bringing the time-scale circuit into operation.

The start-stop teleprinter signals for conversion are fed in from a tape-controlled autotransmitter shown on the left-hand side of Fig. 1. This auto-transmitter is only operative as long as a control potential is applied thereto over lead Ll from Fig. 4. For the present it can be assumed that such a potential is applied. The synchronising pulses are phased and timed so as to coincide with the leading edge of the start element emitted by the auto-transmitter. Thus, the periodicity of the synchronising pulses is determined by the length of the combinations emitted by the auto-transmitter. If the latter is working on a seven-element code basis, the synchronising pulses occur every milliseconds. If on the other hand a seven-and-a-half-element code is in use, the pulses are spaced milliseconds apart.

At 30, 50, 70, 90, and 110 milliseconds, gating potentials are applied to gate G6. These potentials are applied at the theoretical centres of the ve permutable elements of the signal combination. Since othe other input of G8 is from the space lead at the output of the autotransmitter it follows that G6 will give an output of one pulse for each space element in the code combination. These latter pulses will pass through gate Gl to the character register R2. R2 is a non-repeating pattern-movement reglster comprising a plurality of static electrical switches, for example ve cold-cathode gaps interconnected in the manner described in copending application of A. D. Odell, filed March 3, 1950, and bearing Serial No. 147,378. The nonrepeating character of the register is indicated by a circular appendage to the right hand block 3 in the chain. The ve permutable elements of the signal combination are stored successively on tube 1 of R2. Before storage of the first permutable element (at times 3 and 23 milliseconds) and between storage of successive elements (at times 43, 63, 83 and 103 milliseconds) stepping .pulses are gated through gate G8 to step the pattern on R2. vThe tubes. of R2 are left uniired if a mark is received and fired `to record a space. After 1-10 milliseconds the received code combination (i. e. the signal combination less the .start and stop elements) .fis stored as a `pattern on R2, the .rst permutable element .being eventually .registered by the condition of tube 3 on the right of the chain.

Before proceeding further la more detailed description will be given of gate G1, since the nature of this .gate is rather different from those disclosed in said British patent specification No. 636,700 already referred to, although it uses the .same principles.

Gate G1 has two input circuits and rone .output circuit as shown .and the figure lfinside the symbol means ythat either input Yis suiiicient to produce an output. A suitable circuit Ifor achieving this is shown in Fig. 5. The two :in- .put terminals are denoted .l and 2 and the koutput .terminal is denoted 3. Fig. shows also .gas-filled tubes Vi and V2 as illustrations of Aconventional means for applying an input .potential to terminal l and utilising the `output .potential from terminal 3 respectively. The positive voltage applied to the upper end of RI normally causes a current to ilovv through this resistor, rectifier X l, terminal andr-esistor nR3 to earth. Due to the voltage drop across RI, the voltage applied via rectifier X2 and terminal 3 is insuiiicient to Anre gas-discharge tube V2. Resistor .R3 forms the cathode load of la gas discharge gap VI which may be part of a single tube or of a multi-gap tube such as CI, C2 vor vC3 (Fig. l). When gap VI is red, it develops a .potentia1 across R3 which is suiiicient to block rectifier Xi. There is now no current through RI .consequently there is no voltage drop across it. Thus, the full positive potential is available to nre tube V2 which in turn produces a positive voltage output by virtue of the voltage developed across its cathode load resistor R4.

Terminal 2 `is assumed to be yconnected to `a third vgas discharge gap (not shown) in the same manner as terminal l is connected to gap 2, hence if this third gap is tired, and not VI, 'the potential applied to the upper end of R2 will be applied over `rectiier X4 and terminal lil yto fire V2 as before.

The same principle can be extended to more complicated gating arrangements. For example, in Fig. 6 is shown a gating circuit having three inputs, any two ci which will 'suiiice to produce an output. This would be represented symbolically by va circle with three input arrows, one output arrow and a gure 2 in the centre. An example of such a gate is G34 appearing in Fig. 4. Other examples appear in Figs. 9 to 13 to be met With later.

Referring to Fig. 6, it is assumed that the finput terminals G, 5 and f5 are connected to the cathodes of respective discharge devices vin the same manner as terminal l is-con-nected to ydevice V I in Fig. v5. If a blocking potential is simultaneously present on, say, input terminals 44 and 5 then rectiers XE and X1 are blocked and the voltage applied via resistor R5 is passed kthrough rectier XI i to the output terminal 1 which may be conveniently connected tothe trigger of a device such as V2 in Fig. 5. If blocking potentials are present on input terminals 5 `and 6, .rectiers X8 and Xie are blocked and a voltage is passed via resistor R1 and rectier X I3 to the output terminal 1. Similarly, if blocking potentials are 4from gate G21 to register .6 yapplied to input terminals 4 ,and '6, rectiers X6 yandXS are blocked and a voltage is passed to out- Vput terminal 1 viaresistor R6 and rectifier X12. Also appearing in Figs. 1 tori, are gates having three operative inputs Yout of four (e. g. G8 and Gl l in Fig. 1). The circuit for achieving this is Nsomewhat complex but represents a logical .de-

velopment of the circuits of Figs. 5 and 6. It has not, therefore, been considered necessary to show this further circuit.

Returning to Figs. 1 to 4, While the received code combination is being stored on the character register R2, the number .of space elements is ybeing recorded by the space register which is a non-repeating 8-unit `pattern register R3 `(Fig.

3) also .connected as described in said co-pending applicationof A. D. Odell. This register has impressed thereon a .pattern (reading from left to right) as follows M M S M M S S M, that .is to say, tubes 2, 3 and 6 .of the chain are fired and the remainder extinguished. At intervals .of 30, 50, 7), 90 and 110 milliseconds, i. e. in the .theo retical centres of theve permutable elements .of the incoming signal combination-a pulse is passed from gate G28 to gate G2! provided that .at the same time a positive potential is present on lead L2 which is connected to the space lead (Fig. l) and there is a positive potential applied to .gate G20 from F3 (a condition which will be referred to later but which is assumed to be present at this time). Thus, for every space element in the received code combinationiwith-one excep Ation as will beexplained later) one pulse is passed R3. This causes the pattern to progress by one step to the right. yAt intervals of 20, 40, .60, 80, milliseconds from the beginning of the start element-i. e. at the beginning of each permutable element-gate G24 yis opened to allow thefcond-ition of tube l of the register to be repeated by tube s although this does not cause the pattern to progress along the register R3. The number of spaces recorded on thespace register determines the translation to 'be effected in order to produce a seven-element code combination uniquely representative of the original live-element .code combination. Before proceeding further With .the circuit description, a fuller explanation will .be given of the various stages of translation .involved .as shown in the table of Fig. 7.

vIn 'the rst place, since only the ive permutable elements .of an incoming .signal combinationare involved, it is necessary to add two further elements to bring the number .up to the required seven. This is achieved by adding a two-.element ypreiix, the nature of which is shown in the third column. In the cases of combinations ycontaining one, two and three spaces fthe prex merely adds the requisite number of additional spaces to bring ythe seven-element total up to three spaces and 'four marks. In the case .of these combinations no further translation is required andthe transmitted seven-element combination consists of .the `two-element prefix followed y.by the original nvejunit code combination.

lIn the case of the remaining combinations, .namely those containing .no spaces, four spaces and .five spaces, .an invariable lprefix is transmitted which is different from those transmit-ted 'in 'the case .of one-space, two-space and threespace combinations and further translation is necessary to adjust the .number of .spaces to the required number. In the fourth column of the `table of Fig, 7, opposite the nofspace, four-space and five space combinations, are shown the last 7 five elements of the corresponding seven-element combinations. Where a translation has been carried out, the translated elements have been shown within small individual squares.

It is believed that with this explanation, Fig. 'Y is self-explanatory and it will not be referred to again in the course of the description.

It will rst be assumed that the received code combination is one containing one space, for example, M M S M M. When this combination is received, it is registered on the character register R2 (Fig. l) by the firing cf the middle tube only. At the same time, the fact that there is only one space element means that the pattern on register R3 3) is only advanced once and since the space element is the third element to be received, it is the pulse at 70 milliseconds which causes the pattern to be advanced. After this pulse has been passed to R3 the pattern on R3 reads as follows M M M S M M S S. Ten milliseconds later gate G24 is opened to cause tube 8 to assume a spacing condition in agreement with tube I. Tubes I and 2 of R3 continu-e to record two spaces which is the requisite prefix for a code combination containing only 4one space, no other modification or translation being necessary as previously explained.

At 121 milliseconds, gates GIB and G32 (Fig. 1) open to cause the condition of tube I of the space register R3 (Fig. 3) to be passed via lead L6 to tube 2 of the prei-lx register Ri (Fig. l) so that this tube records a space. The prefix register RI is also connected as described in Said co-pending application of A. D. Odell and. so when a stepping pulse is passed via gate Gil at 122 milliseconds, the discharge in the lefthand tube 2 of RI is transferred to the right hand tube I and tube 2 is extinguished. At 122 milliseconds also a stepping pulse is passed.

register R3 causing the pattern thereon to be advanced to read M M M M S M M S.

At 123 milliseconds gates GIO and Gl2 (Fig. 1) again open to cause tube 2 of the prefix register RI to be fired and so to represent a space in accordance with the condition of tube I of the space register R3 (Fig. 3). Both tubes of RI are thus fired to represent a prex of two spaces. rl'he space register R3 receives further stepping pulses at 124, 126, 128, 130, 132, 134 and 136 milliseconds respectively and these stepping pulses merely act to clear the pattern off the tubes I to 8 and leave them all in a nonconducting condition.

If code combinations containing two spaces and three spaces are received, the action is similar to that which has just been described except that the pattern on the space register R3 is advanced by two steps for two spaces and by three steps for three spaces. In the case of a two-space combination, tubes I and 2 of R3 read S M respectively and this is the appropriate prefix which is subsequently transferred to the prefix register RI (Fig. 1). In the case of a three-space combination, the prefix read off R3 and stored on RI is M M. All that remains to be done in the above three cases is to read off and transmit the prefix stored on RI followed by the unchanged code combination stored on R2. This takes place during the receipt of the next code combination.

At 138 milliseconds the stop tube SP of flipop FI (Fig. 1) is red and this, by well-known action, causes the start tube ST to be extinvia gates G21 and G21 (Fig. 3) to the space' ,s convenient transmission path.

guished so that no more pulses go to the timescale circuit. At 138 milliseconds the number of pulses which have been counted by the timescale circuit is 138 5=690. This means that a discharge is present across gaps Il, 9 and 6 respectively of tubes CI, C2 and C3. It is thus necessary to reset only tubes C2 and C3 to the initial condition i. e. with the discharge across gap Il in either tube. This resetting is done by a transient voltage pulse induced when FI changes over to the stop condition.

When the succeeding code combination is received, the time-scale circuit (Fig. 1) is again started into operation as previously described and the first pulse therefrom (the timing of which is indicated as 0) passes through gate GI3 (Fig. 2) to re the mark tube MO of the output flip-flop F2, if it is not already fired. This causes the extinguishing of the space tube 4SO, if this was fired.

The output flip-nop F2, supplies a keying device shown by a block and assumed to be of any Well-known kind. The voutput of this keying ydevice is taken to the receiving device over any For example, the keying device could modulate the phase or amplitude of a carrier wave transmitted over a radio path or it could simply apply marking or spacing potentials to a telegraph line. The

. precise method of transmission is immaterial to the invention.

At a time of 0.2 millisecond later i. e. on the occurrence of the next pulse from the timescale circuit, gate GIA is opened if a potential is present on lead L1. This lead is connected to tube I of the prex register RI (Fig. 1) and a potential is only present on lead L? when tube I is fired to represent space. Thus, if the prefix stored is S M or S S, GIA will be opened at 0.2 millisecond and a pulse will be passed through this gate and gate GIS (which normally receives a second gating inputl from GIB) to fire the space tube SO of the output flipflop F2 and extinguish the mark tube MO. Thus, the output relay changes over to the spacing contact and a space is transmitted for the first element of the prex which is the rst element of the constant total seven-element code combination. If the prefix stored on RI is M M or M S, gate GI4 will not be open and the mark tube MO of the output flip-flop will remain fired.

At l millisecond-i. e. after 5 pulsesgate GII (Fig. 1) is opened to allow a stepping pulse to pass into the prex register RI thus stepping the pattern on RI so that the second elemelrt of the prex is now recorded on tube I of At 2 milliseconds, gate G9 is opened to allow the condition of tube 3 of R2 to be transferred to tube 2 of RI via gate GIil. The third element of the seven-element combination is now registered on tube 2 and the second element on tube I.

At 3 milliseconds, G8 opens to allow a stepping pulse to step the pattern on R2 along by one step so that the last four elements of the sevenelement combination are now registered on tubes 3 to 6 of R2. It will be seen that the original pattern on tubes I to 1 of RI and R2 has advanced by one step to the right in substantially the same manner as if all seven tubes formed a single continuous chain.

At 20 milliseconds gate GI3 (Fig. 2) again opens to cause a pulse to fire tube MO if the the pattern on RI. and R2v is againstepped in-` two stages and thev remaining ve elements are examined and transmitted in sequence, the pattern on RI, R2. being stepped after eachY examination.

It will be noted that the rst two steppingsof the pattern on R2 take place in suilcient time toA allow the rst permutable element of the second code combination4 to be registered on tube 1. of R2.

So far, it has been assumed that the codeA combinations received have contained one, twoor three spaces sothat no translation is neces-- sary beyondthe addition of a prefix which is S S, S M or M M depending on. the number of spaces in the-other ve elementsB Y It will now be assumed. that the.v combination to, be translated is SS S S M namely one-conf taining four spaces, This is recorded on R2 by the firing of tubes 3, 4, 5 and 6. ,Atv the. sam'e time the pattern on R3- `(whichA is` rc3-established` by a potential passed over lea-d L3 every timeV the stopY tube SP isl fired (Fig. 11))v is steppedI by four positions, one After each stepping, the condition ofy tube If is; examined by gate G24 and its condition repeated by tube 8. The progress of the pattern on R3 during the receipt of therst four permuta'bley elements is shown by the followingtablerin-whichr for ease of reading, the numbers of the tubes; rhave been writtenfrom. lef-t to right instead; off

from right to left as they appear in: 3'. It.'

isL to be noted that the only times listed; are

significant onesi. e..times when a-.cha-nge.- in.

the condition of the tubes takes place.`

Tubes l 2 3 .4V 5- 6 7 8 Initial pattern M S S M M S M M 30 ms S S M M S M M S S M M S M M` SE -M- S M M S S M M At 1-01 millisecondsgate iszopen since tubes 5 and 6` are both fired; and a gating` potential is normally presenton lead'- LII)y as will be explainedA later.;` Accordingly, a pulse` is passed to re tube F' of:A a three-stage, trigger device F3. Tube F being redto. representv four spaces, extinguishes the: norma'll tube'A Nv which was-previously red.

At 121 and 123y milliseconds;thelconditionoff tubes I and 2 ofthe space counter R31 is exam-- ined and transferred to tubes I and tof-the pre-- )for each space element.

f gates GH 10 the combination set up on RI, R2 is read off as previously described, the outputl flip-flop F2 (Fig. 2) being bia-assedN to mark every twenty milliseconds and brought back to space 0.2 millisecond later if tube I of` RI isred to denote a space element. This time, however, the ring of the four-space tube F ofv F3 (Fig. 3) acts via lead- L9 and gate G30l (Fig. 3) to open a gate GI'I to pulses occurring at 40.4 and 80.4 milliseconds. Thus, at- 40 milliseconds, F2 is biassed to mark by the firing of MO and at 40.2 milliseconds, SO is -red in accordance With the spacing nature of the third? element, but at 40.4 milliseconds,v MQ is again red by a pulse through and* GI3- that a mark is' sent for the third element instead: of a space. The fourth element issent out without change but the fth element is reversed in the same way at 80.4 milli-k seconds so that the seven-element code combi-i nation finally transmitted is M- S lil S`l\ d` S'v M. There may be a tendency to vibra-tion in the transmitting contacts in the period of 0.4 millisecond at the commencement of the third and ilith elements bu-t it is-vbelievedl that this can be tolerated? for thev sake of simplicity of the' translation circuits thereby resulting.

The code combination .S S S M S- and S M S S- S` eachI containing four spaces are dealt' with.v in aL similar manner to that just described,

the gate G23 bei-ng opened to' operate the tube F' of'FS'v t 1'1-1 milliseconds-L The pre'x M S is in'- serted andj that-bird; and fifthL spa'ce elements of the seven-element combination are replaced before-transmission by mark elements in the same manner as that described. The twol code combinations sent' out are Sl M S M` M S- and M S M L /l S1 S respectively.

Thelother two four-space combinations, namely.- S S' Si S and' M S S S S'- have the same S' prefix insertedl but undergonot only a secon'dbut a third translation before being transmitted. as will now be explained.

Irrthel case ofthe combination S Sv M S S, the- SeVen-element combination` set up on RI', R2 (from right to`l lef-ti is- M S S S' M S- Si The thirdE element (being a space) is converted to a mark as` previously described' at 40.4 milliseconds but the fifth element isalready amark- However;` the-.firing ofthe' four-mark tube F` of F3- (l'ig.-3z)y also opensla; gate GIS (Fig. 2).

Gate GIG acts Via gate G-I5- (-which, as previously stated.. normally receives asecondA input from G-IS at 8024 milliseconds tore the space tube SO so that-a spaceissent for the fth element instead of amar-k;-

It shouldibe'- noted that the gates GIG and G'II arelso'. interconnected with the output flip-nop F2 that; provded the four space tube-F-o'ilipdop-E3. (Fig.` 3;) is red, the third ments of the seven-element code combinationf'set up@ onv Rll,- RZ? will always be reversedy whether they. be markj or space.' Thus, the combination M S M S S SSb'ecomes M- SS S S S and the-combination MS SIS M' S Sibecomes M S S S- S S.- Eachl of thesek combinationscontains morethanj three spaces, so before theyare finally transmitted;v they are subjected to the action of a1 space limiter. after the prefix `has beenlt'ransmitted (whichcontai'ns onespace) only two. more spaces are-sent out,V after which the transmitting. contacts remain on the marking. side for the remaining ele-- spe'etive-of the condition ofy tube for nil' (Fig-1) and fifth elle# This ensuresthat The space limiter (Fig. 2) comprises a threestep, non-repeating, counting chain C4 which may, for example, consist of three, cold-cathode, gas-discharge gaps interconnected in well known manner such that successive pulses applied to all the gaps in common cause the discharge first to pass from gap I to gap 2 and then from gap 2 to gap 3. Initially, and before each combination is transmitted, a discharge is present across gap I, the output of which supplies a potential to open gate GIS.

At 40.6 milliseconds, GI8 is opened if tube SO of the output flip-dop F2 is red, which in turn, means that the third element of the seven-element combination is a space. The opening of gate GIB causes a stepping pulse to be passed to counting chain C4 to cause the discharge to pass from gap I to gap 2. This signifies two spaces (counting the prei-lx) have been transmitted. Since the output of gap 2 also feeds GI9, the latter gate remains open.

At 60.6 and 80.6 milliseconds, the condition of F2 is again examined. If another space element is detected (meaning that the required total of three has been reached), C4 is again stepped and the discharge passes to gap 3. When this occurs, gate GIS is closed thereby closing gate GES. No further space elements can now be transmitted since no voltage can be applied to re the space tube SO after F2 has been biassed to the mark position by the firing of the mark tube MO at the beginning of the next signal element. The combinations M S S l\ S S and M S M S S S thus become M S S S M lt 'l 1 /i and M S M S S M l\ /l, respectively.

When the five-space combination is received for translation it is registered on R2 by the firing of tubes 3 to 'I (Fig. l) and the first four spaces cause the space register R3 (Fig. 3) to step along to give the pattern M M S S M M S M, as previously described. This causes the four-space tube F of F3 to iire and so closes gate G22 and opens gate G25. The closing of gate G21) means that the fth space element does not cause the pattern on R3 to take a further step.

At 110 milliseconds, a pulse passes through gates G25 and G26 to re the all-space/all-mark tube A of trigger device F3. The extinguishing of the four-space tube F removes a potential from lead L9 and cuts off the reversing arrangements and space limiter of Fig. 2.

The firing of tube A opens a gate G29 (Fig. 3) which supplies two outputs, one to gate G28 and the other via lead L to a gate G5 (Fig. 1).

At |22 and |24 milliseconds, the pattern on the space register R3 (Fig. 3) is advanced by two steps and the prefix M S is transferred to the prefix register RI (Fig. 1), as previously described. 'Ihe pattern on R3 thus becomes M M M M S S M M.

At 125 milliseconds, gate G28 is opened and the condition of tube I of R3 transferred over lead L4 and gate GT to tube I of R2 (Fig. 1).

At 126 milliseconds, gate G5 opens to allow a stepping pulse to pass via gate GB to step the pattern on R2. Also at 126 milliseconds, the pattern on R3 is stepped along one step. This process is repeated until the condition of tubes I to 5 of R3 have been transferred to tubes 3 to I of R2 thus driving out the rive-space pattern originally stored on R2. The combination now registered on R, R2 (reading from right to left) is now M S M S S M M and it is this seven-element combination which is transmitted to represent the all-space, code combination.

In the case of the all-mark combination, the original pattern remains on the space register R3 namely, M M S M M S S M. At 111 millisec-f onds, gate G22 (Fig. 3) is opened since tubes 2 and 3 are both fired, a gating potential is assumed to be present on lead LID, and the allspace/all-mark tube A of F3 is fired. The action from then on is the same as described for the all-space combination except that the seven-element combination set up on RIy R2 and subsequently transmitted, is M S S M M S l, which is the pattern originally set up on tubes I to 1 respectively, of the space register R3.

It is to be noted that the all-mark combination will always be the iirst combination to be transmitted when the circuit begins its rst cycle of operations since this code combination is represented when all the tubes of the character register R2 are left unfired. This will have no undesirable effect at a receiving teleprinter since it is usual to preface transmission with the all-mark (letter shift) combination to ensure that the teleprinter is in the right condition to print normal characters in the lower case. The iirst combination received from the auto-transmitter will thus be the second combination to be translated.

The arrangements so far described provide for the conversion of thirty-two start-stop teleprinter code combinations into respective seven-element code combinations having a constant proportion of marks and spaces. It is thus possible at a receiver to detect the presence of an incorrect combination by virtue of the incorrect number of marks and spaces. The arrangements now to be described provide for the transmission after a given number of seven-element combinations of an additional cross-check combination, the respective elements of which are determined from a computation of the corresponding elements in the previous combinations. By this means, it is possible at the receiver not only to detect which combination but which element of that combination, is at fault.

Let it be assumed rst of all, that the crosscheck combination is inserted after only two code combinations have been transmitted. The derivation of the cross-check combination in this case may be seen with the aid of the following example:

Example 1 First combination M S S M M S M (Letter Second combination S S S I\l M M )I Shift) Cross-check combination.. S M M M M S )I Example 2 In practice, it is uneconomical in line-time to insert the cross-check combination after every two combinations and, in general, it is preferred to insert it after, say, five combinations have been transmitted. The same principles of derivation apply, as will be seen from the following example, in which the first two of nve combinations are identical with those used in Examples 1 and 2 already given:

Returning now to Figs. 1 to 4 the cross-check combination is set up on the cross-check register R4 (Fig. 4). This is a seven-unit, non-repeating pattern-movement register of the type already referred to. Initially there is set up on R4, a pattern or combination of seven marks, i. e. tubes I to 'I are extinguished. This represents in the binary notation, a total of zero.

At a time of 6 milliseconds from the starting of the time-scale circuit (Fig. 1), the mark tube M of a nip-flop F (Fig. 4), is red by a pulse passed through a gate G38.

At rI milliseconds, the condition of tube I of the cross-check register R4, is examined by a pulse through a gate G35. If tube I is fired to represent a space, F5 is changed over to space by the nring of tube S.

At 8 milliseconds, the pattern on R4 is stepped l by a pulse applied through a gate`G34, the direction of stepping in Fig. 4 being from left to right.

At 9 milliseconds, a pulse is applied to a gate GSI to examine simultaneously the conditions oi the mark tube M of flip-nop F5 and the space tube SO (via lead LI l) of the output nip-nop F2 (Fig. 2). If both these tubes are fired, G3I provides an output potential which is passed via gates G32 and G33 to nre tube 'I of the cross-check register R4. Thus, a space will be inserted in the pattern on R4 each time a space (on F2) is added to a mark (on F5).

At 10 milliseconds, a pulse is applied to a gate G3'I to examine simultaneously the conditions of the space tube S of flip-flop F5 and the space tube SO (via lead LiI) of the output flip-flop F2 (Fig. 2). If both these tubes are nred, G31 provides an output potential which is passed via gate G38 to re-re the mark tube M of flip-flop F5. Thus, a mark `will be recorded on F5 each time a space (on F2) is added to a space (on F5).

At 11 milliseconds the condition of the space tube S of nip-flop F5 is examined by a pulse applied through a gate G38 and if the space tube is still red, a potential is passed via gates G32 and G33 to nre tube I of the cross-check register R4. Thus, a space is recorded in tube 'I if a space on F5 is added to a mark on F2 since the fact that F5 is still in the space condition implies that F2 is in the marking condition.

At 26, 46, 66, 86, 106 and 126 milliseconds, the foregoing cycle of events isrepeated so that by 131 milliseconds the pattern set up on R4 represents the addition of the original combination stored thereon and the constant-total code combination transmitted by the output relay F2 (Fig. 2).

At 136 milliseconds, the flip-flop F5 is biassed to mark via gate G38.

At 13.7 milliseconds, the condition of tube I of 14 the cross-check register R4 is examined via gate G35. If tube I is fired to signify a space, this fact is recorded by the ring of the space tube of F5.

It should be noted that the last two times mentioned, occur after the iinal stepping of the pattern on R4 so that the ultimate condition of tube I of R4 is recorded by the ultimate condition of flip-flop F5.

The operation of the circuit in setting up the cross-check combination has now been described in general terms. The operation of this part of the circuit will, it is believed, be more readily understood by a consideration of what actually takes place when two sample combinations are added together. For convenience the two combinations chosen are those quoted in Example l already given. Furthermore, it has been considered preferable to set out the various steps in tabular form in Fig. 8 rather than to incorporate them into the text.

Referring now to Fig. 8, it is to be observed rst of all, that the only times which have been listed in the nrst column are significant times i. e. times at which a change takes place in the condition of either of the flip-flops F2 and F5 or in the condition of the cross-check register R4. The line corresponding to time 0 represents the conditions obtaining at the beginning of each cycle.

The broken lines and bracketed symbols in the second column (representing the condition of the output nip-flop F2) have been inserted to give a truer picture of the seven-element combinations being transmitted although it will be appreciated that there lwill be no significant change in the condition of the output relay between successive elements of the same kind.

In order to give a truer picture of the combinations set up on R4, the order of the tubes in Fig. 8 has been reversed from that shown in Fig. 4. Thus, in Fig. 8 the direction of stepping is from right to left.

With the foregoing explanation it is believed that Fig. 8 will be readily understandable.

It will be seen from Fig. 8 that at the end of the first cycle, the combination set up on R4 is the same as the rst combination sent out from F2. The reason for this will be obvious when it is recalled that the original "all-mark setting on R4 represents a total of zero in binary notation.

At the end of the second cycle the combination set up on R4 will be seen to' be identical with that obtained theoretically in Example 1.

Fig. 8 shows in detail how the cross-check combination is derived from two previous code combinations. In practice, as already explained, this number is too few and the circuit of Figs. 1 to 4 is arranged to insert' the crossecheck combination after every ve code combinations. It is, however, considered to be unnecessary toshow in the detailed form of Fig. 8y how nve code combinations are added togetherto produce corresponding cross-check combination.

'I'he arrangements nowl to be described pro-- vide for the stopping of the auto-transmitter after nve code combinations have been sent out andv for the transmission of the cross-check character derived in the manner already explained.

The counting of the five code combinations is done by a six-unit counting chain C5 (Fig. 4)'. Before the first combination is transmitted, this counting chain is set in a condition where the first gap 0 is nred, the remaining gaps being extinguished. This may be achieved by momentarily operating the make-before-break contacts KI. The firing of gap 0 results in the firing of the normal tube N of a nip-flop F4. The output of tube N supplies potentials to various gates, the numbers of which will be apparent from the drawings and also via lead LI, it supplies a potential to cause the auto-transmitter (Fig. 1) to send code combinations into the character register R2.

At 138 milliseconds, after the commencement of the iirst cycle of operations, a pulse from source P- (Fig. 4 )is gated through a gate G30 to step the discharge in counting chain C5 from gap 0 to gap I and so to record that one combination has been transmitted. Similarly, at the end of the second combination, the discharge passes to gap 2 and at the end of the th combination gap 5 is tired.

rIhe ring of gap 5 results in the firing of the check tube C of F4 and the extinguishing of the normal tube N. The firing of tube C causes gating potentials to be applied to gates G39 and G40, whose purpose will be explained later.

The extinguishing of tube N has the following results:

(a) By removing a potential from lead LI it stops the auto-transmitter (Fig. l) from sending any further code combinations into the character register R2.

(b) By removing a potential from lead LIU, it disables certain gates (the numbers of which will be readily apparent from the drawings) and so ensures, inter-alia, that nothing alters the composition of either the code combination stored on the character register R2 (Fig. l) or of the cross-check combination stored on register R4 (Fig. 4).

The next synchronising pulse applied to gate GI (Fig. l) starts the time-scale circuit again and the first pulse produced thereby lres the mark tube MO of the output ilip-ilop F2 (Fig. 2) by means of gate GI3.

The next pulse from the time-scale circuit causes gate GI4 to examine the condition of f.

lead LI2 connected to gate G39 (Fig. 4) which is, in turn, arranged to examine the condition of flip-flop, F5. It has already been explained that after the cross-check combination has been set up on R4, ilip-op F5 is caused to assume a condition representative of the condition of tube I of R4. Thus. when GI4 (Fig. 2) is opened at 0.2 millisecond, it effectively examines the condition of tube I of R4 on which tube is registered the first element of the cross-check combination. If this rst element proves to be a space, the space tube SO of the output relay F2 (Fig. 2) is fired.

At 4 milliseconds gate G40 opens and supplies an input to gate G34. This, in turn, causes a stepping pulse to pass into the cross-check register R4 and so the pattern on R4 takes one step to the right. The second element of the cross-check combination is now recorded on tube I of R4.

At 6 milliseconds the mark tube M of nip-flop F5 is red via gate G38.

At 7 milliseconds the condition of tube I of the cross-check register R4 is examined by a pulse through gate G35. If tube I is fired to represent a space, F5 is changed over to space by the firing of tube S. The second element of the cross-check combination is now registered by the condition of ip-flop F5.

At 8 milliseconds the pattern on R4 is stepped by a pulse through gate G34, gate G40 taking no further part in the operation. The third element of the cross-check combination is now recorded on tube I of R4.

At 2() milliseconds the mark tube of the output ip-flop F2 (Fig. 2) is iired.

At 20.2 milliseconds the second element of the cross-check combination is read oir flip-flop F5 by means of gates GI4 and G39 and the output flip-flop F2 is conditioned accordingly.

The remaining elements of the cross-check combination are read oir and transmitted in a similar manner, the condition of tube I of R4 being repeated by flip-flop F5 after each stepping of the pattern on R4. lThe last two stepping pulses clear the pattern off R4 and leave it in its initial condition with all tubes extinguished.

The counting chain C5 is of the repeating type so that the next pulse at 138 milliseconds steps the discharge from gap S back to gap 0. This results in the changing-back of flip-flop F4 to the normal condition with tube N fired. The re-connection of an operating potential to lead LI causes the re-starting of the auto-transmitter (Fig. 1) and the combination already stored on R2 is translated and sent out.

Since the number of code combinations sent out before the cross-check combination is determined solely by the counting chain C5, it will be apparent that this may be replaced, if desired, by a counting chain having, say, seven positions, in which case the cross-check combination would be inserted after every six code combinations. The actual number chosen would depend, for example, upon the amount of interference likely to be encountered but should not be too small for the reasons already given. Appropriate changes would also be necessary at the receiver, the nature of which changes will be apparent later. It is clear, also that such changes at transmitter and receiver can be made from time to time by agreement between the two stations to suit the interference conditions arising, for example, during diierent periods of transmission.

Referring now to the arrangements for reception and decoding shown in Figs. 9 to 13, the incoming seven-element code combinations arriving over lead LIS (Fig. 9) pass to a receiving device indicated generally by a labelled block. The contents of this receiving device will depend upon the nature of the communication medium between transmitter and receiver. As far as this invention is concerned, it is only necessary that the receiving device shall produce marking or spacing potentials at its output in accordance with the signals received from the transmitter.

Synchrcnising signals are received from the transmitter over line LI4 (or some analogous communication medium) and pass to a gate G4I. The first synchronising pulse fires the start tube ST of a flip-nop FII so extinguishing the stop tube. The output o1 tube ST supplies a gate G42 and so brings into operation a time scale circuit comprising three multi-cathode counting tubes Cl I, CI2 and CI3, and three gating tubes G42, G43 and G44. This time scale circuit is similar to that shown in Fig. 1 and serves a similar purpose, namely, to time the various operations which take place.

At 10 milliseconds, the condition of the marl: lead from the receiving device is examined by a gate G45 the third input to which is supplied from the normally fired tube N of the flip-nop 

